The present invention relates to the field of valves for gas handling systems, and more particularly, to a valve seat assembly providing a highly reliable gas-tight seal.
In the art of valves for gaseous systems, obtaining an effective seal between the movable valve element and the valve seat is an essential requirement. To obtain an effective seal, in U.S. Pat. No. 3,489,171 of Michael, et. al., a soft gold metal valve seat is permanently preformed under the pressure of the valve element. The theory is that the preformed seat is thus assured of conforming to the shape of the element during valve use. In U.S. Pat. No. 3,106,219 of Teston, a soft metal alloy seat is likewise used to provide a seal with a metal ball valve element. In the two patents cited above, successful operation of the valve is dependent upon the non-elastic deformation of the valve seat resulting from the flow of the valve seat metal when in contact with the valve element under pressure. In both patents, permanent deformation of the valve seat metal occurs during operation of the valve.
Permanent deformation, however, presents a difficulty when, during routine maintenance procedures, an original valve element is replaced by a new valve element. It is difficult to provide an adequate gas seal between a new valve element and a previously permanently deformed metal valve seat. To rework a permanently deformed valve seat requires great effort with particular attention being paid to valve element alignment, concentricity, surface finish, seating angle, and stroke distance.
Another approach for providing valve seals for gaseous systems is the use of a resilient O-ring such as disclosed in U.S. Pat. No. 2,963,262 of Shafer and U.S. Pat. No. 3,548,869 of Weise, et. al. A serious problem associated with the use of an O-ring is the possibility of a blow-out under high pressure conditions. Another problem associated with the use of an O-ring is contamination of the gas in the system by the material from which the O-ring is fabricated, usually organic polymeric materials. This contamination is especially undesirable in gas handling systems for high purity gases used for instrument calibration.